Homeowners in the United States spend $1 out of every $8 of utility costs on cooling their living space. Window air conditioners (A/Cs) are an inexpensive alternative to central systems and are sold in greater numbers each year than all other residential cooling systems. They are bought to cool a specific room, are inexpensive to purchase, and are easy for anyone to install. But these benefits come at a cost. Window A/Cs operate less efficiently than most other residential cooling systems, and they may not provide equivalent comfort.